INTRODUCTION. XOV11 



with the necessary thoroughness would require a much 

 larger space than I have at my command. I must con- 

 tent myself with referring the student for detailed infor- 

 mation on these branches of the subject to the works of 

 Allman, Smitt, Nitsche, MetschnikofF, Claparede, Hat- 

 schck, Vogt, Salensky, Repiachoff, Joliet, and (chiefly) 

 Barrois *, who has specially devoted himself to this de- 

 partment, and has given us, in a splendid monograph, a 

 M-rics of admirable and exhaustive researches. 



The larvae, which are developed from the ova, and 

 jive rise to the first term of the polyzoan colony, pre- 

 sent many varieties of form and a somewhat complex 

 structure (see Plate LXXXIII.). The figures on this 

 Plate will give some idea of the singularity of shape, 

 the beauty of colour, and the profusion of ciliary and 

 flagellate appendages which they frequently exhibit. The 

 forms represented in figures 9 and 10 are also furnished 

 with a delicate bivalve shell. The larvae are restless in 

 their habits, and during their short term of free exis- 

 tence are in almost constant movement, now whirling 

 rapidly hither and thither, now tumbling over and over in 

 the water, now creeping along, making use of their cilia 

 as feet. Besides their ciliary appendages, they are often 

 furnished with long setiform processes, which wave to 

 and fro, and lash the water with much vehemence. After 

 a while their energies fail, and they settle down and be- 

 come attached ; the cilia begin to flag in their movements, 

 and soon disappear ; and the volatile and curiously orga- 

 nixcd beinjj resolves itself into a fixed and (apparently) 

 homogeneous mass, in which the first zooecium and poly- 

 j)ide originate. 



* The titles of the respective works will be found in the Bibliographical 



the flow of tins volume. 



h 



